In case of fixing device for electro-photographic image forming apparatus such as copiers, printers etc., toner image is fixed on paper by passing paper through a nip between a pair of rollers consisting of a heat roller and a press roller, or similar belts. In such a fixing device, a phenomenon that a portion of the toner image sticks to the heat roller at the time of fixing, may take place, and the toner stuck to the heat roller is further transferred to the press roller, so that the press roller is suffered from corruption. For this reason, a device is provided in which a metallic cleaning roller is pushed on the press roller to remove the toner stuck to the press roller and the toner is deposited on the surface of the cleaning roller.
On the other hand, in such a fixing device, a phenomenon that particle of calcium carbonate which is a composition of paper sticks to the press roller at the time of fixing takes place. As the particle is apt to stick to the toner, especially when the European paper or Chinese paper etc. which contains a large quantity of calcium carbonate is used, a phenomenon that particle of calcium carbonate in the paper is mixed with the toner stuck to the surface of the press roller and the mixture sticks to the press roller takes place.
As the stuck toner mixed with the particle calcium carbonate forms balls and the stickiness is weak, the toner sticks again to the press roller after cleaning by the cleaning roller and, as the result, paper may suffer from corruption. Or the cleaning performance of the cleaning roller may be reduced. Furthermore, in case of Chinese paper, rough calcium carbonate of irregular shape is contained often. For example, there has been a case that the number of detected rough particles of calcium carbonate that are more than 20 μm in length was 1,204 pieces/cm2.
The stuck toner that is mixed with such rough particles of calcium carbonate of irregular shape can be recovered hardly by a cleaning roller and deposited on the surface of the press roller and, as the result, the press roller and paper are suffered from corruption. Or the cleaning performance of the cleaning roller may be reduced. Also, when the heat roller and the press roller are pressed each other, as the rough particles of irregular shape, consisting of calcium carbonate and the stuck toner exist on the surface of press roller, the surface of the heat roller may cause dents. As the result, the smooth surface of the heat roller is roughed. The roughed surface of the heat roller reduces the shape-separating performance of the heat roller. As the result, the toner stuck to the heat roller from the toner image at the time of fixing increased, and the quality of the image was deteriorated due to the drop of the fixing performance and/or corruption of paper.
For this reason, as shown in Japanese Patent Application Publication No. 2001-312173, there is an apparatus that the toner stuck to the press roller is removed completely by utilizing both a cleaning roller that removes the toner stuck to the surface of the press roller and a cleaning brush that removes the adhesion from the press roller such as particles of calcium carbonate.
However, in case of the cleaning brush laid open by Japanese Patent Application Publication No.2001-312173, the cleaning brush is located in the upper stream of the cleaning roller in the turning direction of the press roller. Such being the case, when the particles of calcium carbonate on the press roller are removed, the toner stuck to the press roller is caught by the cleaning brush that contacts at first. For this reason, when the paper which contains a large quantity of calcium carbonate is used, cleaning brush is pushed to the press roller and mainly particles of calcium carbonate are removed by the cleaning brush. On the other hand, when paper containing a small volume of calcium carbonate is used, the cleaning brush is separated from the press roller, in order to prevent that the toner with strong adhesion stuck to the cleaning brush is transferred to the press roller. As in this case, a construction that the contact position of the cleaning brush can be changed against the press roller is provided. Such being the case, there is a problem that the mechanism supporting the cleaning brush becomes complicated in the case of the fixing device laid open by Japanese Patent Application No. 2001-312173.